Study of controlling phase separation in Yb3+-doped fluorophosphate glasses via molecular dynamics simulations

Abstract

Yb3+-doped fluorophosphate (FP) glasses are considered to be important laser glass materials with wide application prospects. However, fluorine phase separation greatly affects the lasing properties of the materials. Besides, understanding the phase separation mechanism of FP glass and finding practical methods to control it remain unsolved problems. Herein, we study the phase separation of Yb3+-doped FP glass with the compositions of P2O5-Al2O3CaF2-YbF3 based on molecular dynamics simulations. The results reveal immiscible behaviors that the glass separates into fluoride-rich phase and aluminophosphate-rich residual matrix. The Al3+ coordinated with both O2− and F− form the [Al(O,F)n] polyhedrons on oxide-fluoride interface. Furthermore, to understand the structure of Al3+ dependent glass phase, we generate a series of FP glasses by replacing Ca2+ with Al3+. Those models indicate that [Al(O,F)n] polyhedron plays an important role in breaking the connection of fluoride-rich regions, preventing the further growth of fluoride phase and stabilizing the double-phase structure effectually.